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package java.lang.reflect;

import java.lang.annotation.Annotation;

import java.lang.annotation.AnnotationFormatError;

import java.lang.annotation.Repeatable;

import java.util.Arrays;

import java.util.LinkedHashMap;

import java.util.Map;

import java.util.Objects;

import java.util.function.Function;

import java.util.stream.Collectors;

import sun.reflect.annotation.AnnotationSupport;

import sun.reflect.annotation.AnnotationType;

/**

 * Represents an annotated element of the program currently running in this

 * VM.  This interface allows annotations to be read reflectively.  All

 * annotations returned by methods in this interface are immutable and

 * serializable. The arrays returned by methods of this interface may be modified

 * by callers without affecting the arrays returned to other callers.

 *

 * <p>The {@link #getAnnotationsByType(Class)} and {@link

 * #getDeclaredAnnotationsByType(Class)} methods support multiple

 * annotations of the same type on an element. If the argument to

 * either method is a repeatable annotation type (JLS 9.6), then the

 * method will "look through" a container annotation (JLS 9.7), if

 * present, and return any annotations inside the container. Container

 * annotations may be generated at compile-time to wrap multiple

 * annotations of the argument type.

 *

 * <p>The terms <em>directly present</em>, <em>indirectly present</em>,

 * <em>present</em>, and <em>associated</em> are used throughout this

 * interface to describe precisely which annotations are returned by

 * methods:

 *

 * <ul>

 *

 * <li> An annotation <i>A</i> is <em>directly present</em> on an

 * element <i>E</i> if <i>E</i> has a {@code

 * RuntimeVisibleAnnotations} or {@code

 * RuntimeVisibleParameterAnnotations} or {@code

 * RuntimeVisibleTypeAnnotations} attribute, and the attribute

 * contains <i>A</i>.

 *

 * <li>An annotation <i>A</i> is <em>indirectly present</em> on an

 * element <i>E</i> if <i>E</i> has a {@code RuntimeVisibleAnnotations} or

 * {@code RuntimeVisibleParameterAnnotations} or {@code RuntimeVisibleTypeAnnotations}

 * attribute, and <i>A</i> 's type is repeatable, and the attribute contains

 * exactly one annotation whose value element contains <i>A</i> and whose

 * type is the containing annotation type of <i>A</i> 's type.

 *

 *

 * <ul>

 *

 * <li><i>A</i> is directly present on <i>E</i>; or

 *

 * <li>No annotation of <i>A</i> 's type is directly present on

 * <i>E</i>, and <i>E</i> is a class, and <i>A</i> 's type is

 * inheritable, and <i>A</i> is present on the superclass of <i>E</i>.

 *

 * </ul>

 *

 * <li>An annotation <i>A</i> is <em>associated</em> with an element <i>E</i>

 * if either:

 *

 * <ul>

 *

 * <li><i>A</i> is directly or indirectly present on <i>E</i>; or

 *

 * <li>No annotation of <i>A</i> 's type is directly or indirectly

 * present on <i>E</i>, and <i>E</i> is a class, and <i>A</i>'s type

 * is inheritable, and <i>A</i> is associated with the superclass of

 * <i>E</i>.

 *

 * </ul>

 *

 * </ul>

 *

 * <p>The table below summarizes which kind of annotation presence

 * different methods in this interface examine.

 *

 * <table class="plain">

 * <caption>Overview of kind of presence detected by different AnnotatedElement methods</caption>

 * <thead>

 * <tr><th colspan=2 scope="col">Method</th>

 *     <th colspan=4 scope="col">Kind of Presence</th>

 * <tr><th scope="col">Return Type</th>

 *     <th scope="col">Signature</th>

 *     <th scope="col">Directly Present</th>

 *     <th scope="col">Indirectly Present</th>

 *     <th scope="col">Present</th>

 *     <th scope="col">Associated</th>

 * </thead>

 * <tbody>

 * <tr><td style="text-align:right">{@code T}</td>

 * <th scope="row" style="font-weight:normal; text-align:left">{@link #getAnnotation(Class) getAnnotation(Class&lt;T&gt;)}

 * <td></td><td></td><td style="text-align:center">X</td><td></td>

 * </tr>

 * <tr><td style="text-align:right">{@code Annotation[]}</td>

 * <th scope="row" style="font-weight:normal; text-align:left">{@link #getAnnotations getAnnotations()}

 * <td></td><td></td><td style="text-align:center">X</td><td></td>

 * </tr>

 * <tr><td style="text-align:right">{@code T[]}</td>

 * <th scope="row" style="font-weight:normal; text-align:left">{@link #getAnnotationsByType(Class) getAnnotationsByType(Class&lt;T&gt;)}

 * <td></td><td></td><td></td><td style="text-align:center">X</td>

 * </tr>

 * <tr><td style="text-align:right">{@code T}</td>

 * <th scope="row" style="font-weight:normal; text-align:left">{@link #getDeclaredAnnotation(Class) getDeclaredAnnotation(Class&lt;T&gt;)}

 * <td style="text-align:center">X</td><td></td><td></td><td></td>

 * </tr>

 * <tr><td style="text-align:right">{@code Annotation[]}</td>

 * <th scope="row" style="font-weight:normal; text-align:left">{@link #getDeclaredAnnotations getDeclaredAnnotations()}

 * <td style="text-align:center">X</td><td></td><td></td><td></td>

 * </tr>

 * <tr><td style="text-align:right">{@code T[]}</td>

 * <th scope="row" style="font-weight:normal; text-align:left">{@link #getDeclaredAnnotationsByType(Class) getDeclaredAnnotationsByType(Class&lt;T&gt;)}

 * <td style="text-align:center">X</td><td style="text-align:center">X</td><td></td><td></td>

 * </tr>

 * </tbody>

 * </table>

 *

 * present on an element <i>E</i> is computed as if indirectly present

 * annotations on <i>E</i> are directly present on <i>E</i> in place

 * of their container annotation, in the order in which they appear in

 * the value element of the container annotation.

 *

 * <p>There are several compatibility concerns to keep in mind if an

 * annotation type <i>T</i> is originally <em>not</em> repeatable and

 * later modified to be repeatable.

 *

 * The containing annotation type for <i>T</i> is <i>TC</i>.

 *

 * <ul>

 *

 * <li>Modifying <i>T</i> to be repeatable is source and binary

 * compatible with existing uses of <i>T</i> and with existing uses

 * of <i>TC</i>.

 *

 * That is, for source compatibility, source code with annotations of

 * type <i>T</i> or of type <i>TC</i> will still compile. For binary

 * compatibility, class files with annotations of type <i>T</i> or of

 * type <i>TC</i> (or with other kinds of uses of type <i>T</i> or of

 * type <i>TC</i>) will link against the modified version of <i>T</i>

 * if they linked against the earlier version.

 *

 * (An annotation type <i>TC</i> may informally serve as an acting

 * containing annotation type before <i>T</i> is modified to be

 * formally repeatable. Alternatively, when <i>T</i> is made

 * repeatable, <i>TC</i> can be introduced as a new type.)

 *

 * <li>If an annotation type <i>TC</i> is present on an element, and

 * <i>T</i> is modified to be repeatable with <i>TC</i> as its

 * containing annotation type then:

 *

 * <ul>

 *

 * <li>The change to <i>T</i> is behaviorally compatible with respect

 * to the {@code get[Declared]Annotation(Class<T>)} (called with an

 * argument of <i>T</i> or <i>TC</i>) and {@code

 * get[Declared]Annotations()} methods because the results of the

 * methods will not change due to <i>TC</i> becoming the containing

 * annotation type for <i>T</i>.

 *

 * <li>The change to <i>T</i> changes the results of the {@code

 * get[Declared]AnnotationsByType(Class<T>)} methods called with an

 * argument of <i>T</i>, because those methods will now recognize an

 * annotation of type <i>TC</i> as a container annotation for <i>T</i>

 * and will "look through" it to expose annotations of type <i>T</i>.

 *

 * </ul>

 *

 * <li>If an annotation of type <i>T</i> is present on an

 * element and <i>T</i> is made repeatable and more annotations of

 * type <i>T</i> are added to the element:

 *

 * <ul>

 *

 * <li> The addition of the annotations of type <i>T</i> is both

 * source compatible and binary compatible.

 *

 * <li>The addition of the annotations of type <i>T</i> changes the results

 * of the {@code get[Declared]Annotation(Class<T>)} methods and {@code

 * get[Declared]Annotations()} methods, because those methods will now

 * only see a container annotation on the element and not see an

 * annotation of type <i>T</i>.

 *

 * <li>The addition of the annotations of type <i>T</i> changes the

 * results of the {@code get[Declared]AnnotationsByType(Class<T>)}

 * methods, because their results will expose the additional

 * annotations of type <i>T</i> whereas previously they exposed only a

 * single annotation of type <i>T</i>.

 *

 * </ul>

 *

 * </ul>

 *

 * <p>If an annotation returned by a method in this interface contains

 * (directly or indirectly) a {@link Class}-valued member referring to

 * a class that is not accessible in this VM, attempting to read the class

 * by calling the relevant Class-returning method on the returned annotation

 * will result in a {@link TypeNotPresentException}.

 *

 * <p>Similarly, attempting to read an enum-valued member will result in

 * a {@link EnumConstantNotPresentException} if the enum constant in the

 * annotation is no longer present in the enum type.

 *

 * <p>If an annotation type <i>T</i> is (meta-)annotated with an

 * {@code @Repeatable} annotation whose value element indicates a type

 * <i>TC</i>, but <i>TC</i> does not declare a {@code value()} method

 * with a return type of <i>T</i>{@code []}, then an exception of type

 * {@link java.lang.annotation.AnnotationFormatError} is thrown.

 *

 * <p>Finally, attempting to read a member whose definition has evolved

 * incompatibly will result in a {@link

 * java.lang.annotation.AnnotationTypeMismatchException} or an

 * {@link java.lang.annotation.IncompleteAnnotationException}.

 *

 * @see java.lang.EnumConstantNotPresentException

 * @see java.lang.TypeNotPresentException

 * @see AnnotationFormatError

 * @see java.lang.annotation.AnnotationTypeMismatchException

 * @see java.lang.annotation.IncompleteAnnotationException

 * @since 1.5

 * @author Josh Bloch

 */

public interface AnnotatedElement {

    /**

     * Returns true if an annotation for the specified type

     * is <em>present</em> on this element, else false.  This method

     * is designed primarily for convenient access to marker annotations.

     *

     * <p>The truth value returned by this method is equivalent to:

     * {@code getAnnotation(annotationClass) != null}

     *

     * <p>The body of the default method is specified to be the code

     * above.

     *

     * @param annotationClass the Class object corresponding to the

     *        annotation type

     * @return true if an annotation for the specified annotation

     *     type is present on this element, else false

     * @throws NullPointerException if the given annotation class is null

     * @since 1.5

     */

    default boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {

        return getAnnotation(annotationClass) != null;

    }

   /**

     * Returns this element's annotation for the specified type if

     * such an annotation is <em>present</em>, else null.

     *

     * @param <T> the type of the annotation to query for and return if present

     * @param annotationClass the Class object corresponding to the

     *        annotation type

     * @return this element's annotation for the specified annotation type if

     *     present on this element, else null

     * @throws NullPointerException if the given annotation class is null

     * @since 1.5

     */

    <T extends Annotation> T getAnnotation(Class<T> annotationClass);

    /**

     * Returns annotations that are <em>present</em> on this element.

     *

     * If there are no annotations <em>present</em> on this element, the return

     * value is an array of length 0.

     *

     * The caller of this method is free to modify the returned array; it will

     * have no effect on the arrays returned to other callers.

     *

     * @return annotations present on this element

     * @since 1.5

     */

    Annotation[] getAnnotations();

    /**

     * Returns annotations that are <em>associated</em> with this element.

     *

     * If there are no annotations <em>associated</em> with this element, the return

     * value is an array of length 0.

     *

     * The difference between this method and {@link #getAnnotation(Class)}

     * is that this method detects if its argument is a <em>repeatable

     * annotation type</em> (JLS 9.6), and if so, attempts to find one or

     * more annotations of that type by "looking through" a container

     * annotation.

     *

     * The caller of this method is free to modify the returned array; it will

     * have no effect on the arrays returned to other callers.

     *

     * @implSpec The default implementation first calls {@link

     * #getDeclaredAnnotationsByType(Class)} passing {@code

     * annotationClass} as the argument. If the returned array has

     * length greater than zero, the array is returned. If the returned

     * array is zero-length and this {@code AnnotatedElement} is a

     * class and the argument type is an inheritable annotation type,

     * and the superclass of this {@code AnnotatedElement} is non-null,

     * then the returned result is the result of calling {@link

     * #getAnnotationsByType(Class)} on the superclass with {@code

     * annotationClass} as the argument. Otherwise, a zero-length

     * array is returned.

     *

     * @param <T> the type of the annotation to query for and return if present

     * @param annotationClass the Class object corresponding to the

     *        annotation type

     * @return all this element's annotations for the specified annotation type if

     *     associated with this element, else an array of length zero

     * @throws NullPointerException if the given annotation class is null

     * @since 1.8

     */

    default <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {

         /*

          * Definition of associated: directly or indirectly present OR

          * neither directly nor indirectly present AND the element is

          * a Class, the annotation type is inheritable, and the

          * annotation type is associated with the superclass of the

          * element.

          */

         T[] result = getDeclaredAnnotationsByType(annotationClass);

         if (result.length == 0 && // Neither directly nor indirectly present

             this instanceof Class && // the element is a class

             AnnotationType.getInstance(annotationClass).isInherited()) { // Inheritable

             Class<?> superClass = ((Class<?>) this).getSuperclass();

             if (superClass != null) {

                 // Determine if the annotation is associated with the

                 // superclass

                 result = superClass.getAnnotationsByType(annotationClass);

             }

         }

         return result;

     }

    /**

     * Returns this element's annotation for the specified type if

     * such an annotation is <em>directly present</em>, else null.

     *

     * This method ignores inherited annotations. (Returns null if no

     * annotations are directly present on this element.)

     *

     * @implSpec The default implementation first performs a null check

     * and then loops over the results of {@link

     * #getDeclaredAnnotations} returning the first annotation whose

     * annotation type matches the argument type.

     *

     * @param <T> the type of the annotation to query for and return if directly present

     * @param annotationClass the Class object corresponding to the

     *        annotation type

     * @return this element's annotation for the specified annotation type if

     *     directly present on this element, else null

     * @throws NullPointerException if the given annotation class is null

     * @since 1.8

     */

    default <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass) {

         Objects.requireNonNull(annotationClass);

         // Loop over all directly-present annotations looking for a matching one

         for (Annotation annotation : getDeclaredAnnotations()) {

             if (annotationClass.equals(annotation.annotationType())) {

                 // More robust to do a dynamic cast at runtime instead

                 // of compile-time only.

                 return annotationClass.cast(annotation);

             }

         }

         return null;

     }

    /**

     * Returns this element's annotation(s) for the specified type if

     * such annotations are either <em>directly present</em> or

     * <em>indirectly present</em>. This method ignores inherited

     * annotations.

     *

     * If there are no specified annotations directly or indirectly

     * present on this element, the return value is an array of length

     * 0.

     *

     * The difference between this method and {@link

     * #getDeclaredAnnotation(Class)} is that this method detects if its

     * argument is a <em>repeatable annotation type</em> (JLS 9.6), and if so,

     * attempts to find one or more annotations of that type by "looking

     * through" a container annotation if one is present.

     *

     * The caller of this method is free to modify the returned array; it will

     * have no effect on the arrays returned to other callers.

     *

     * @implSpec The default implementation may call {@link

     * #getDeclaredAnnotation(Class)} one or more times to find a

     * directly present annotation and, if the annotation type is

     * repeatable, to find a container annotation. If annotations of

     * the annotation type {@code annotationClass} are found to be both

     * directly and indirectly present, then {@link

     * #getDeclaredAnnotations()} will get called to determine the

     * order of the elements in the returned array.

     *

     * <p>Alternatively, the default implementation may call {@link

     * #getDeclaredAnnotations()} a single time and the returned array

     * examined for both directly and indirectly present

     * annotations. The results of calling {@link

     * #getDeclaredAnnotations()} are assumed to be consistent with the

     * results of calling {@link #getDeclaredAnnotation(Class)}.

     *

     * @param <T> the type of the annotation to query for and return

     * if directly or indirectly present

     * @param annotationClass the Class object corresponding to the

     *        annotation type

     * @return all this element's annotations for the specified annotation type if

     *     directly or indirectly present on this element, else an array of length zero

     * @throws NullPointerException if the given annotation class is null

     * @since 1.8

     */

    default <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass) {

        Objects.requireNonNull(annotationClass);

        return AnnotationSupport.

            getDirectlyAndIndirectlyPresent(Arrays.stream(getDeclaredAnnotations()).

                                            collect(Collectors.toMap(Annotation::annotationType,

                                                                     Function.identity(),

                                                                     ((first,second) -> first),

                                                                     LinkedHashMap::new)),

                                            annotationClass);

    }

    /**

     * Returns annotations that are <em>directly present</em> on this element.

     * This method ignores inherited annotations.

     *

     * If there are no annotations <em>directly present</em> on this element,

     * the return value is an array of length 0.

     *

     * The caller of this method is free to modify the returned array; it will

     * have no effect on the arrays returned to other callers.

     *

     * @return annotations directly present on this element

     * @since 1.5

     */

    Annotation[] getDeclaredAnnotations();

}